Scuba divers carry one or more tanks of compressed air or mixed gas for diving. In order to enable the divers to breathe normally underwater, the gas pressure should be reduced to an ambient pressure. Regulators are used to reduce the gas pressure to an ambient pressure, typically in two stages. The first stage regulator typically reduces the gas pressure from about 2,500 to 3,500 psi to about 150 psi. The second stage regulator further reduces the gas pressure to an ambient pressure.
For each breathing cycle, the high-pressure gas flows through the first stage regulator valve orifice. As the compressed gas flows through the valve of the first stage regulator it rapidly expands and flows through a low-pressure hose to the second stage regulator. This rapid drop of the pressure and expansion of the gas at the first stage regulator causes a substantial decrease of the temperature of the gas. As the gas travels through the second stage regulator, the gas pressure is reduced again when it changes from about 150 psi to ambient pressure, which causes additional cooling in the second stage.
Since the housing and the valve of the second stage regulator may be cooled to below freezing temperatures, ice may build up on the surfaces of the cooled parts, which may prevent proper operation of the device. This can result in reduced performance or complete failure of the second stage. In addition, breathing the cold air (at a much lower temperature than ambient) increases respiratory heat loss and thermal stress to the diver. For these reasons, it is highly advantageous to warm up the gas flowing into the second stage regulator to prevent icing and failure of the second stage.
A heat exchange device has been used to warm up the pressurized gas exiting the first stage regulator. For example, U.S. Patent Application Publication No. 2002/0179089 to Morgan et al. discloses a heat exchange device for use with the underwater pressurized gas source. FIG. 1 of the present application shows the heat exchange device disclosed in the Morgan application. The heat exchange device in the Morgan application includes a length of tubing 8. The gas exiting the first stage regulator 14 flows through the tubing 8 toward the manifold block 18 while being warmed up by the ambient water surrounding the tubing 8. The gas then flows through outlet tubes 22 via outlet ports 20 of the manifold block 18 to the second stage regulator. The tubing 8 is made of heat conducting material for facilitating heat exchange.
In the heat exchange device that is disclosed in the Morgan application, one end of the tubing 8 is connected to the first stage regulator 14 through an inlet tube 16. The other end of the tubing 8 is connected to the manifold block 18. Breathing gas exiting the first stage regulator 14 enters the tubing 8 through an inlet port 17, and the breathing gas exits the tubing 8 through an outlet port 19. The inlet port 17 and the outlet port 19 are in different locations, spaced apart from one another.
In Morgan's heat exchange device, the air entering the tubing 8 is extremely cold, so that it is subject to freezing at the inlet port 17. Consequently, ice may start to build up around the inlet port 17 and the portion of the tubing 8 that is close to the inlet port 17. This significantly reduces the efficiency of the heat exchange device.
Therefore, there is a need for a more efficient heat exchange device for warming up compressed air from a pressurized air source that is being used in connection with underwater diving equipment.